The present invention relates to an intake apparatus of an internal combustion engine for a vehicle such as motorcycle and, more particularly, to an intake apparatus having an opening and closing portion of the butterfly type structure arranged at a suction port of an air cleaner.
Conventionally, in an air cleaner arranged on the intake side of an internal combustion engine, there has been known a technology for controlling the opening and closing of a suction port of the air cleaner so as to change an air intake condition of the internal combustion engine.
First, such a technology is disclosed in the Japanese Utility Model Publication No. SHO 59-13333. In the technology of this publication, a movable member for opening and closing the suction port is actuated by means of a negative-pressure motor in accordance with an engine rotational speed to attain the improving of fuel consumption and the increasing of an output power of the internal combustion engine.
Further, in the above-mentioned technology, there have been also known a diaphragm type, a rod type and a valve type ones adapted to open and close an intake passage, which are disclosed in the Japanese Utility Model Publication No. SHO 58-51409. That is, in the technology of this publication, a diaphragm is moved in accordance with a change of a negative pressure on the downstream side of an engine throttle valve and a valve is opened and closed by means of a negative pressure motor through a rod in accordance with that movement to reduce a suction noise.
Furthermore, the above-mentioned technology is also disclosed in the Japanese Patent Laid-open Publication No. SHO 63-239350, in which a shutter is arranged at an opening portion of an air cleaner and the opening and closing of the shutter are controlled by an electronic control unit (ECU) depending on factors representing a running condition of an internal combustion engine so as to adequately control a fuel-air ratio.
In such prior arts, however, although an area of the suction port of the air cleaner is variable in accordance with the rotational speed of the engine, a variation of an output power of the internal combustion engine is large because the area of the suction port is controlled suddenly by the ON/OFF operations of the negative-pressure motor (i.e. diaphragm) due to the characteristics thereof.
Especially, when the suction port is changed over from a small opening area to a large opening area, an increase of the output power is so large that a riding feeling happens to be affected badly.
In the case of the ECU controlling like in the last mentioned prior art, since only the rotational speed of the engine is used as the control parameter and other informations are not employed, it is impossible to carry out fine control.